Earplugs formed solely of soft resilient foam material are difficult to insert into the ear canal. When the front end of the earplug lies against the entrance to the ear canal and the rear end of the earplug is pushed, the foam earplug collapses. During such collapse, as shown at Z in FIG. 15, the front end of the earplug enlarges in diameter and does not move into the ear canal. It has been found that a core of stiffer material, as in the form of a rod, can be placed in a soft resilient foam body to help insert the foam body into the ear canal. U.S. Pat. No. 5,573,015 by Williams shows a foam body molded around a stiffer core by extrusion.
Although an earplug with a stiffener that is exposed is acceptable to many people, an earplug with stiffener that is almost completely covered by the soft foam material of the body is often more acceptable, at first. The largely concealed stiffener does not remind a person that stiff material is to be inserted into his/her ear canal and raise fears (unfounded) of discomfort by the presence of stiff material. Thus, an earplug with a largely concealed stiffener would be of value. A method for forming such earplug with a largely concealed stiffener also would be of value.
Although a rod-shaped elastomeric stiffener helps in earplug insertion, it makes the earplug stiffer against bending. Many people have ear canals that are curved, so an earplug inserted into one of the ears must bend to follow the curvature of the ear canal. The stiffener resists bending, causing forces on the sides of the person's ear canal and consequent possible discomfort to the person. An earplug with a stiffener to help insertion, wherein the stiffener was sufficiently stiff against column collapse but was easily bent by the walls of the ear canal to avoid discomfort, would be of value.
Methods for establishing a stiffer of any desired shape in a mold cavity, at low cost, also is desirable.